Exhaust silencer



March 31, 1936. L L, HAAS EXHAUST SILENCER Filed Sept. 21, 1932 3 Sheets-Sheet 2 March 31, 1936. L L HA EXHAUST SILENCER Filed Sept. 21, 1932 s sheets-sheet 3 Patented Mar. 31, 1936 UNITED STATES PATENT OFFICE EXHAUST SILENCE]!- Lucien L. Haas, Buflalo, N. Y., assignor to Butfalo Pressed Steel Company, Buffalo, N. Y.

This invention relates to improvements in mufflers or silencers for the exhaust of internal combustion engines.

The objects of this invention are to provide muillers of improved construction in which the greater part of the exhaust gases can pass directly through the muiiler without change in direction of flow; also to provide a muffler of this kind in which the various sound waves present in the exhaust can be reduced to the required extent by means of a series of chambers of improved construction arranged about the central passage through the mufller; also to provide a sound deadening chamber near the discharge end of the muilier with means of improved construction for producing passage of gas therethrough to evaporate liquid discharged into this chamber; also a muffler shell with perforations elongated in the direction of flow of the gases 20 past the perforations to eliminate a whistling or hissing sound; also to improve mufilers of this kind in other respects herein disclosed.

In the accompanying drawings:

Fig. 1 is a longitudinal central sectional ele- 25 vation of a muilier embodying this invention.

Figs. 2, 3, and 4 are similar longitudinal central sectional elevations of mufflers of modified construction.

Fig. 5 is a transverse sectional elevation of the 30 mufiler shown in Fig. 4 on line 55, Fig. 4.

Figs. 6, '7, and 8 are longitudinal central sectional elevations of mufflers of modified constructions.

Fig. 9 is a transverse section on an enlarged 35 scale, on line 9-9, Fig. 8.

It has been known for some time that sound waves passing throughperforated tubes, if the tube extends through a medium having the property of absorbing sound, will be destroyed or reduced to a sufficient extent so as not to be ohjectionable. Various sound absorbing materials have been used in connection with mufflers of this kind, but most of these materials have been found unsatisfactory for the reason that the exhaust 45 gases of internal combustion engines contain certain liquid and gaseous materials which cause rapid corrosion of such sound absorbing materials. In accordance with this invention, certain sound deadening chambers containing no sound ab- 50 sorbing material are provided about the perforated central passage or duct through the muffler, in which chambers the various sound waves are absorbed or broken up. Certain gases passing through such chambers are cooled by contact 55 with the outer walls of the muffler and by returning these cooled gases to the main stream of gases flowing through the mufller, a further sound deadening effect is produced.

In the muffler shown in Fig. l, 9 represents the outer shell of the muiller which is provided at the 5 inlet end thereof with a head I0 and the discharge end with a head I I, all of these parts being of usual construction, the inlet head being provided with the usual tubular extension to which the exhaust pipe from the engine may be 10 connected and the discharge head Ii is provided with a corresponding extension to which the tail pipe may be secured. I2 represents an inner shell of the muiller which is suitably connected with the inlet head, for example, by means of a connecting member l4, one end of which is connected with a shoulder of the inlet head l0 and the other end of which has a telescopic engagement with the adjacent end of the inner shell l2. The inner shell is perforated either throughout the entire length thereof or the greater portion of this shell is perforated, and the perforations may be of any suitable or desired form, but it has been foundthat if these perforations are in the form of elongated slits I5 extending lengthwise of the direction of flow of the gases through the inner shell, the usual whistling or hissing noise in the inner shell is eliminated, which noise results when perforations of circular and other forms are used.

The discharge end of the inner shell l2 may be supported within the muflier in any suitable manher, and in the construction shown, two baifles i6 and ll are provided which are arranged in the space between outer and inner shells, and which, therefore, support the inner shell with reference to the outer shell.

The space between the baffle i6 and the inlet head l0 preferably contains one or more intermediate shells, two such shells l8 and 19 being illustrated in the construction shown. Preferably these shells are arranged concentric with the inner shell, and are made tapering or of frusto-conical shape, so that the chambers formed between adjacent shells will be of greater cross sectional area at one end thereof than at the other end, and the gases are preferably caused to flow in these chambers in the direction of their length from the larger toward the smaller end. It has been found that this ar- 5 rangement has a compressing efiect upon the sound waves which results in a very efiective deadening of these waves. In the construction shown, the inlet shell 12 is also made of tapering form, having the largest end nearest to the than at the inlet end, which results in a building up of slight pressure at the inlet end. I utilize this slight pressure to provide a circulation of gas through the chambers formed about the inner shell of the muiller, but it will be understood that this invention is not intended to be limited to muiliers having inner shells tapered in this manner.

Because of the slight pressure built up at the inlet end of the inner shell, it will be obvious that some of the gases at the inlet portion of the inner shell will flow through the perforations or slits l5 into the chamber between the inner shell i2 and the intermediate shell l8, and such gases will flow lengthwise in this chamber and will then pass outwardly through discharge apertures 20 arranged in the end of the shell l8 nearest to the discharge end of the muiiier. The gases passing outwardly through the discharge apertures 26 will enter the chamber between the shells l8 and i3 at the larger end of this chamber and will flow toward the smaller end thereof, and then through apertures 2| in the shell These apertures admit the gases into the larger end of a chamber formed between the outer shell 9 and the intermediate shell l9, and the gases will consequently flow lengthwise of this chamber toward the smaller end thereof and through apertures 22 in the baflle l6. In flowing from the larger to the smaller end of a chamber, the sound waves will be subjected to a compressing action which produces a mui'fling of the same. Preferably, the outer chamber of the series is divided into two parts by means of a transverse bafile 24 arranged between the shells 9 and i9 to further reduce sound waves in this chamber.

In the passage through the outer chamber and in contact with the outer shell 8 of the muiller, the gases will be decidedly cooled and these 'cooled gases are discharged into a chamber formed between the baffles l6 and I1 and the inner and outer shells of the muffler. It will be noted that the portion of the inner shell passing through this chamber is perforated and, consequently, gases are free to pass through these perforations, and also sound waves which have not been absorbed in the portion of the inner shell passing through the intermediate shell i8, will pass through the perforations into the chambers formed between the bailles i6, i1 and head II and will be destroyed in these chambers. These two chambers are connected by apertures 25 in the baffle l1. s

In the construction shown in Fig. 1, the inner shell I2 terminates short of the discharge passage 26 through the head II and the rapid flow of gases from the end of the inner shell toward the discharge 26 will set up an ejector action in the cylindrical portion 21 of the head ii, and thus draw into the stream of gas any gases contained in the chamber between the head Ii and bafiie n. This ejector action also stimulates the flow of gas in the two chambers at the discharge end of the muiller and may cause some gases from the inner shell to pass through the perforations of this shell into the chamber between the bafiles i6 and I1, and thus mix with the gases discharged from the elongated chambers through the apertures 22 in the baflle IS. The

apertures, in which case this part of the tube will produce an increased suction or vacuum in the chamber between the baiiie i1 and the head The munier shown in Fig. 2 is quite similar to that shown in Fig. 1. In this construction, the outer shell 30 has heads 3| and 32 at its opposite ends, the head II at the inlet end of the mufller having only one shoulder which supports the intermediate shell '33 and a connecting member 34 for the inner perforated shell 35. Only one intennediate shell is used in this construction, which terminates at a transverse baffle 36. A second transverse baflie 31 is spaced between the baiiie 38 and the head 32 of the muiiler. The cylindrical connection 38 for the tail pipe of the muifler may also be formed as a part of the head 32, and an inwardly extending flange or part 33, which engages the inner shell 36 near the discharge end thereof may also be carried by this head. The discharge end of the inner shell terminates at a distance from the tail pipe connection 33 so that an ejector action is produced by the gases discharged from this inner shell to provide for drawing gases through apertures 40 formed in the inwardly extending flange 39. This induces a flow of gases through the sound absorbing chambers formed between the bailles 36 and 31 and the head 32. The operation of the muiiler is substantially the same as the one shown in Fig. 1.

In the construction shown in Fig. 3, the outer shell 43 extends throughout the length of the muiiler and its opposite ends are closed by heads 44 and 45. This muiller also has a continuous straight passage through the same, and the inner shell or duct in this case is built in a number of sections. The first section 46 of this shell is made substantially cylindrical or without taper, and another section 41 of this shell is made tapering toward the discharge end of this muffler to provide for a material difference in pressure at the two ends thereof, both of these sections being of perforated metal. A short central duct or passage 48 is formed on a bafile 49 which supports the ends of a pair of inner shells 50 and 5!, the tube or passage 48 being slightly smaller in diameter than the portion 46 of the inner shell, to provide for a slight difference in pressure tending to cause gases to how through the chambers formed by the shells 56 and 5|. The portion 46 of the inner shell terminates short of the intermediate shell 50 and is spaced therefrom by means of a baffle member 53 having apertures therein, so that some of the gases discharged through the perforations of the part 46 of the inner shell may flow through the apertures in the baille 53. The portion 46 of the inner shell, therefore, discharges its gases into a chamber formed in the end of the intermediate shell 56 between the bafiles 49 and 53, and this portion of the intermediate shell is provided with apertures 54 through which gases and sound waves may pass into the larger end of the tapering chamber between the shells 50 and 5|. The shell 5| is provided with discharge apertures 55 through which gases pass into the larger end of the chamber between the intermediate shell 5i and the outer shell 43. The gases pass from the portion of larger cross section to the portion of smaller cross section in both of these chambers and are then discharged through this chamber through apertures 56 formed in the baffle 49. The second part of the muffler is formed between two ballies 60 and which support the portion 41 of the inner shell and also an inter- I mediate shell 62. A space or chamber is formed between the baffles 49 and 60 in which gases discharged through the apertures 58 may flow toward the axis of the muffler to mix with the gases passing directly through the mufller through the passage 48. This flow of cold gases crosswise of the hot gases produces a further silencing effect on the noise of the exhaust.

A part of the gases discharged through the perforations of the portion 41 of the inner shell pass into the space between this shell and the intermediate shell 62 and flow in this space toward the portion of least cross sectional area and pass out of this space or chamber through apertures 63 formed in the intermediate shell 62. These gases then pass lengthwise of the chamber formed between the intermediate shells 52 and the outer shell 43 and are discharged through apertures 64 in the baffle 6| into the smaller end of the space between this baffle and the head 45. The portion 41 of the inner shell terminates adjacent to the head 45 but out of engagement therewith, thus forming an annular passage between this end of the inner shell and the head 45 through which gases may pass through the discharge aperture of the head.

Another form-of muffler is shown in Fig. 4, in which an outer shell 10 is provided at opposite ends with heads H and 12, and adjacent to the head II at the inlet end of the muffler a baffle 13' is provided, spaced from the inlet head 'II and forming a chamber into which the gases may initially pass on entering the muffler. The baffle 13 is provided with an aperture with which a tapering inner shell 14 cooperates to receive gases.

In this construction a tandem arrangement of mufflers is shown, in that another muffler is provided near the discharge end of the outer shell Ill, and the gases entering the inlet chamber of the muffler are divided, a part of the gases passing to each muffler. A tube or passage 15 terminating at one end in the baffle 13 and at its other end in a baffle 16 conducts gas from the inlet chamber of the muffler to the second muffler. 11 represents an intermediate shell of the first muffler and is secured at one end to the baffle 13 and at the other end to a baffle 18. The shell 11 is provided with gas discharge apertures "Land the other discharge apertures are provided in the baffie 18. The baffle 18 is spaced from a baffle 8| forming between these two baffles a chamber 82 into which gases enter from the apertures 80. The gas from this chamber enters the inner shell 14 through apertures 83 formed in a straight portion of this shell at the chamber 82, and the remainder of this shell is in the form of an imperforate tube and passes through the second muffler and terminates in a baffle 85 near the discharge end of the muliler, so that the portion of the gas entering the inner shell 14 receives all of its mufliing in the front part of the muffler, and is then conducted into a discharge chamber 86 formed between the baffle 85 and the head 12, from where it passes into the tail pipe (not shown).

The portion of the gases which pass through the pipe or duct 15 and are silenced in the rear part of the muffler pass into a chamber between the baffle 15 and a baffle 01 and then enter into a perforated inner shell 88. Most of the gases pass through this shell directly into the discharge chamber 86. Some of the gases pass through the perforations of this shell into a chamber between this shell and an intermediate shell 89, and thence through apertures 90 in this intermediate shell into a chamber between this shell and the outer shell 10. From this chamber, the gases discharge through apertures 9| in the ballle 85 and pass into the discharge chamber 86 of the mulller.

In the case of this muffler, the portion of the outer shell 10 between the baffles ill and 16 may be omitted, in which case the two mufflers will be separate and will be connected only by imperferate portions of the passages I4 and 15.

The muilier shown in Fig. 6 is provided with an inner shell which tapers toward the inlet end of the muffler, the taper being in the reverse direction of the inner shells described in connection with the Figs. 1 to 4. Otherwise, the muffler is of substantially the same construction as the muliler shown in Fig. 2. Even in the construction shown, there is sufficient difference in pressure at the two ends of the inlet shell 95 to cause a certain percentage of the gases to flow through the several chambers formed by the intermediate shell 96 and by the several baffles 91 and 98 and the heads of the muffler. The action of the chambers about the perforate inner shell on sound waves are substantially the same as in connection with the other constructions described, so that a very effective muflling results.

The construction shown in Fig. 7 is somewhat like that shown in Fig. 2, except that the baffle I00 of this muffler is imperforate, so that any gases passing through the perforations of the inner shell |0l into the chamber between this shell and the intermediate shell I02 will pass through apertures I03 into the chamber between the shell I02 and the outer shell I04, and from this chamber the gases pass back to the intermediate chamber through apertures I05, and thence through the perforations of the inner shell to mix with the gases flowing through the inner shell.

At the discharge end of this muffler, a sound deadening chamber is provided between the baffle I00 and the head H15 of the muffler, and an extension l D! of the inner shell, which extension, how ever, is imperforate and arranged in this chamber and held in place therein by means of a baffle H18 in such a manner as to leave an annular space between the discharge end of the portion fill of the inner shell and the portion fill thereof. A similar annular passage is formed at the discharge end of the part fill of the inner shell, thus forming an ejector action at this end of the shell which draws gas through the sound deadening chamber between the baffles I80 and I95, the baffle I08 being provided with apertures I09 for the passage of such gases. The annular passages for the gases and the chamber l l9 have a decided sound absorbing effect in this muffler, and fur-- thermore, the passage of gases through the chamber at the discharge end of the muffler serves the further purpose of evaporating any liquid which might condense and collect in the chamber l 50 of the muffler and at the same time produce cross currents of cool gases at the discharge end of the part ID! of the inner shell, thus further increasing the muffling effect.

In the construction shown in Figs. 8 and 9, a muffler is shown which is built in two parts or sections, as are the muiilers shown in Figs. 3 and 4. In Fig. 8, a single inner shell or tube I I5 is provided which probably tapers from the inlet end of the muffler to the discharge end thereof. The inner shell H5 is perforated near the inlet end thereof and the perforated portion is enclosed by an intermediate shell I I 6 about which is arranged an outer shell I", heads H8 and H9 being provided at the ends of the outer shell. An annular spacing member I 20 is secured to the intermediate shell H6 and forms a support for the inlet end of the inner shell I I 5. The intermediate shell IIIi may be of uniform diameter thoughout its length since the tapered shell 5' forms with the intermediate shell a chamber which decreases in cross sectional area toward the inlet portion of the muffler and apertures I2I in the intermediate shell permit the gases topass into the chamber between this shell and the outer shell. A baille I22 supports the discharge end of the intermediate shell from the outer shell and this bailie is provided with apertures I23 through which gases may pass into a space or chamber I 24 between the baffle I22 and the head I I9. In this chamber, the sound waves are compressed to deaden the sound. A further sound deadening chamber I25 is preferably provided between the inner and intermediate shells and between the baffle I22 and a baffle I26 positioned between the intermediate and inner shells. Apertures I2'I in the bafile I22 establish a communication between the two sound deadening chambers I 24 and I25, so that gases may pass from the former to the latter chamber and then through the apertures in the inner shell which face the chamber I25. By the provision of these different chambers, different sound waves are effectively destroyed.

The second portion of the muffler is somewhat similar to the first portion except that in this case a baille I29 supports the rear end portion of the inner shell H5. The arrangement of the shells and bafiies is such as to form chambers I30 and I3I corresponding substantially to chambers I24 and I25 which have already been described, except that in this case gases are withdrawn from the chamber I3I by the ejector action of the discharge end of the inner shell II5 which is spaced from a cylindrical portion I32 of a baffle I33, so that the discharge of gas from the inner shell will tend to draw gas out of the chamber I3I which in turn causes gas to flow from the cham ber I30 to the chamber I3 I, and consequently also induces a flow of gas in the cylindrical chambers arranged about the inner and intermediate shells.

In all of the constructions described, the perforations in the inner shell have the property of breaking up the sound waves by permitting parts of these sound waves to pass into the several chambers formed about the perforated portions of the inner shell. It has been found that longitudinal passages between the inner, intermediate and outer shells have the property of absorbing and deadening a certain type of species of sound waves while other chambers formed between transverse bailies have a similar effect upon other types of sound waves. By the combination of these chambers as described, a very effective mutiiing of the sound waves is produced with very little back pressure, since most of the gases, of course, flow directly through the inner shell from the inlet to the discharge of the muflier.

I claim as my invention:

1. A mufiler having a direct passage therethrough from the inlet to the discharge end thereof through which exhaust gases may flow without change of direction, said passage including an inner shell provided substantially throughout the length thereof with perforations and tapered toward its outlet end, an outer shell, and an intermediate shell arranged between said inner and outer shells, a pair of transverse baiiles between said inner and outer shells, two of said shells forming between them and with one of said baflies a tapering chamber, means for causing gases passing outwardly through the apertures of said passage to flow in said chamber from the larger to the smaller end thereof, and means for returning gases passed through said chamber to said passage at a point further along that passage, said pair of transverse baifles between said inner and outer shells forming with the inner and outer shells a chamber surrounding a perforated portion of said inner shell, and means for conducting gas to said last mentioned chamber from the smaller end of said tapering chamber.

2. A muffler having a direct passage therethrough from the inlet to the discharge end thereof through which exhaust gases may flow without change of direction, said passage including an inner shell provided substantially throughout the length thereof with perforations, an outer shell, and an intermediate shell arranged between said inner and outer shells and of less length than said outer shell, heads closing the space between said inner and outer shells, and a baffle located between the head at the discharge end of said muffler and the end of said intermediate shell and forming with said inner and outer shells a chamber for gases, apertures in said intermediate shell to permit gases to flow lengthwise in the chambers formed between said shells, and passages for causing a circulation of gases in said chamber between said bailie and head at the discharge end of the mufiler.

3. A mufiler including an outer shell and heads at the inlet and discharge ends of said shell, said muiiler having an inner shell forming a direct passage substantially therethrough from the inlet to the discharge head thereof, through which passage exhaust gases may flow without change of direction, said passage having a portion adjacent the discharge end of lesser cross-sectional area than the opposite end a baiiie arranged intermediate of said heads and connecting said inner and outer shells, said inner shell extending through said bafile and provided throughout the greater portion of the length thereof with perforations which are elongated in the direction of the flow of gases in said shell, an intermediate shell arranged between said inner and outer shells and between said bafiie and one of said heads, said shells forming a series of chambers arranged one within another and surrounding said passage, said intermediate shell having openings solely adjacent one end through which gases discharged through said perforations of said inner shell may flow, and means for producing a circulation of gases in the space between said baflle and the other head of the muiiler.

4. A muflier having an outer and an inner shell, said inner shell being provided with perforations substantially throughout the length thereof, a pair of baffles between the ends of said shells, and an intermediate shell extending from one of said baffies to one end of said muiiier, said inner shell forming at least a part of an unobstructed passage through said mufiler, said intermediate shell forming with said one of said baiiles and the outer and inner shells, a plurality of chambers arranged about the axis of the muflier in which gases can flow lengthwise of said muflier at one side of said one baflle, said intermediate shell being apertured only adjacent the inlet end of said muifler to connect said chambers in series and a chamber extending from the inner to the outer shell being formed at the other side of said baflle, said one bailie being apertured to connect the outermost of the first mentioned chambers to the last mentioned chamber, the other of said bailies being apertured to pass gases, the exit end of said passage having a Venturi section connected to the chamber section between the said other baffle and the adjacent end of said outer shell.

5. A mufller comprising an elongated, imperforate casing, a tube passing from end to end thereof and forming a direct, free passage therethrough, which in cross-sectional area is smaller adjacent its outlet end than at its inlet end, and then expanded, an elongated shell surrounding and extending in a direction endwise of said tube and within said casing, said shell being tapered with its smaller end adjacent the inlet end of said casing and forming with the tube and casing two telescopic, but oppositely tapered, approximately annular. chambers, said tube being apertured at a plurality of intervals along its length, and said shell being apertured solely adjacent its smaller end, and the smaller end of the outer chamber being connected to said tube at the expanded zone of the tube, whereby the expanding gases leaving the smaller area of the tube will create a suction in said outer chamber and draw gases through said chambers in succession.

6. A mufiier having an outer and an inner shell, said inner shell being provided with perforations at intervals along the length thereof, said inner shell being substantially straight from end to end but having its cross-sectional area in a section adjacent its outlet end smaller than at the section adjacent the inlet end,and with the ends of the outer shell forming a continuous passage through the muiiler, said passage beyond said smaller section of the inner shell having a portion larger than said smaller section a baflie between the ends of said shells, and an intermediate shell extending from said baflie to one end of said mufller, said intermediate shell forming with the inner and outer shells, concentric chambers arranged about the axis of the mufiier in which gases can flow in a direction lengthwise of said mufller at one side of said baflle, said intermediate shell being apertured only adjacent the inlet end of said muiiier to connect said chambers inseries, the space between the inner and outer shells and disposed between said baiile and the other end of the mufiler, constituting another chamber, said bafiie being apertured to connect the outermost of the first mentioned chambers to the last mentioned chamber, and said last mentioned chamber communicating directly with said passage at the larger section of said passage beyond that section of said passage having said smaller crosssectional area of the inner shell.

7. A muflier comprising a. tubular casing with a header at each end, and with an opening through each header, the opening at the inlet end of the casing having a greater cross-sectional area than the opening at the outlet end, and the opening at the outlet end of the casing being flanged to provide an outlet passage, a tapered tube having a direct passage from end to end, its larger end connected to the inlet header of said casing and communicating with the opening therein, with the tube extending along the interior of and generally spaced from said casing and terminating at its smaller end in proximity to the opening in the outlet header, the outlet header forming with the small end of the tube and with the outlet passage a relatively short chamber of greater crosssectional area than the adjacent portions of said tube and of said outlet passage, a baflie extending transversely across the interior of said casing approximately between said tube and said casing, an intermediate shell disposed insaid casing and around said tube, largely spaced from both tube and casing, and connected at one end to said baflle and at its other end to the inlet header,

said tube having apertures arranged along its length, said intermediate shell being apertured adjacent the inlet header and imperforate for the remainder of its length, and said bailie being apertured in the portion between said intermediate shell and casing and being imperforate between said intermediate shell and said tube, and the chamber between said casing and tube at the side of said baille opposite from said intermediate shell having communication with said expansion chamber at the outlet end of said tube.

8. In a muflier, a tubular casing having an inlet header at one end and an outlet header at the other end, each header having an opening therethrough, a tube extending through said casing substantially between said headers and open from end to end, said tube having apertures therein at intervals along the same from end to end, the tube with the headers forming a direct passage through said casing, the inlet header and adjacent end of said tube together forming a relatively short passage section having a substantially larger cross-sectional area than of the opening in the inlet header and of the entrance end of said tube, whereby the gases entering said tube through said inlet header will be caused to eddy by said section of greater cross-sectional area and thus caused to impinge to a greater extent against the wall of the tube and pass to a greater extent through said apertures, the space between said tube and easing being subdivided into separate chambers connected in series with one another by restricted passages and to said direct passage adjacent the outlet end thereof, whereby a portion of the gases passing outwardly from said tube through said apertures may pass through said chambers and then return to said passage, and other portions may pass into one of said chambers and return to said passage further along the same.

9. In a mufiier, a tubular casing having an inlet header at one end and an outlet header at r the other end, each header having an opening therethrough, a tube extending through said casing substantially between said headers and open and tapered from end to end, said tube having apertures therein at intervals along the same from end to end, the tube with the headers forming a direct passage through said casing, the inlet header and adjacent end of said tube together forming a relatively short passage section having a substantially larger cross-sectional area than of the opening in the inlet header and of the entrance end of said tube, whereby the gases entering said tube through said inlet header will be caused to eddy by said section of greater cross-sectional area and thus caused to impinge to a greater extent against the wall of the tube and pass to a greater extent through said aper- 1y spaced from the peripheries of the casing and tube and extending iromlone or said headers to the nearest baffle, said shell being apertured solely adjacent said one of the headers and said nearest baille being apertured solely between said shell and casing, the other baille being also apertured, whereby a portion of the gases passing through said apertures in the tube may pass in series through the chambers formed by the said tube, shell and casing, and then return to the tube, and another portion may return directly to said tube from the chamber between said shell and tube.

10. In a muffler, a tubular casing having an inlet header at one end and an outlet healer at the other end, each header having an opening therethrough, a tube extending through said casing and forming with the header a gas passage, open directly from end to end, said tube having apertures therein at intervals along the same in an endwise direction, said passage at the inlet end having a relatively short section of materially greater cross-sectional area than the adjacent sections of the passage, whereby the gases entering said tube through the inlet header will be caused to eddy by the section of greater cross-sectional area and thus caused to impinge to a greater extent against the wall of the tube and pass to a greater extent through said apertures, a baflle disposed across the casing intermediate or its ends and through which the tube closely passes, a shell within and spaced from the casing and surrounding and spaced from the tube and connecting the inlet header with said baille, said shell being apertured adjacent the inlet header and imperi'orate for the remainder of the length thereof, said baflle being apertured between the shell and the casing and impertorate in the space between the shell and tube, said passage at the outlet end having a relativeLv short section oi! greater cross-sectional area than the adjacent portion of the tube and the outlet opening in the outlet header, whereby the gases about to leave said passage will expand in said last named section of greater cross-sectional area, said passage being apertured at said last mentioned section of greater cross-sectional area to provide communication, with that section 01 the passage, of the chamber between said casing and tube and the battle and outlet header, whereby the suction in the expansion chamber at the outlet end will draw gases from the chamber between the outlet header and the baille, and induce movement of some of the gases in series through the chambers formed by the tube and shell and by the shell and casing, in the section between the baille and inlet header, and thence pass through-the chamber between the baiile and outlet header.

LUCIEN L. HAAS. 

